1. Field of the Invention
The present invention relates generally to RF communication systems, and particularly, to a system and method for integrating voice and data on common RF channels using the same equipment in a manner which can significantly increase its flexibility and spectral efficiency.
2. Discussion of the Prior Art
Currently, many land mobile radio system provide both voice/data communication by establishing two essentially independent subsystems within each vehicle: one for voice and one for data. By dedicating separate equipment and RF channels to each type of communication, the resulting system duplicates equipment, wastes RF spectrum, and proves inflexible (because they cannot easily accommodate new types of growing mobile communication such as mobile data terminal (MDT), mobile facsimile, or automatic vehicle location (AVL); nor can they efficiently respond to changes in the mix of voice and data traffic.
For example, Mobile Data Terminals are utilized in many dispatch-related applications to allow mobile users to access remote databases. Uses include logging and tracking packages for delivery services, as well as accessing license plate and driver""s license information for public safety. AVL and mobile fax applications also produce data traffic. It would be highly desirable to integrate voice and data onto common RF channels, as costs pertaining to all interactive applications may be minimized by providing highly efficient transmission facilities, rather than having separate channels for voice and data.
Further, in the broadcast environment especially for dispatch-related applications, it is often desirable for a dispatcher to be able to broadcast a request to an entire group of users, and for any member of the group to be able to either participate in the conversation or to listen to all parties involved in the conversation. For this reason, separate channels are used for uplink (mobile-to-base station) and downlink (base-to-mobile) communications. The base station may thus transmit both halves duplex of a conversation over the downlink channel without interfering with the corresponding uplink channel or transmission. The radios in the mobile units cannot simultaneously transmit and receive, thus during conversation, the mobile user depresses a push-to-talk button to switch the mobile radio from receive to transmit mode whenever the mobile user wishes to speak.
Current systems for voice/data land mobile radio must be changed to take advantage of the new technology, such as facsimile (fax), Remote Database Login, AVL, and unlimited other applications.
Because congestion within the 450 MHz-800 MHz region limits present systems"" capabilities to meet the demand for increased capacity that new services require. One solution to this problem is to allocate new frequency bands, but there is high competition for new frequency allocations, and, in any case, such allocations will be at higher frequencies. High frequencies will propagate weaker signals and require more expensive equipment to enhance performance.
It would then be highly desirable to provide a voice/data communication system that utilizes the current RF frequency region (450 MHz-800 MHz) by integrating voice/data using the same RF channels in a manner so as to increase the voice capacity, and additionally providing full capacity for data communications.
The present invention is directed to a system and method for integrating voice/data on a single RF channel. Central to the system is a dynamic multiplexing technique known as Packetized Data, Voice Dedicated (PDVD) Burst Switching with Lookahead, a signal processing technique used to provide forward information of the silence gaps (speech energy gaps) in the transmitted speech.
According to the principles of the invention, there is provided a system and method for integrating data and voice on a common RF communications channel utilized for mobile radio communications, the system comprising: a means for dividing the common RF channel into at least two voice paths, each path divided into a plurality of fixed-length slots; a means for digitizing speech messages and organizing the messages into variable-length packets; a means for digitizing data messages from one or more data sources into fixed-length size packets, a packet corresponding in size to a fixed-length slot; a voice activity detector for detecting silence gaps in a digitized speech message, and communicating locations of slots in the voice path corresponding to the detected silent gaps to the data sources; and, a means for dynamically multiplexing the variable-length speech packets and fixed-length data packets in slots belonging to a voice path for transmission over the RF channel, the fixed-length data packets being embedded in said slots at locations corresponding to the detected silent gaps of the speech.
Advantageously, the Integrated Voice/Data System may be retrofitted into existing 450 and 800 MHz public and private land mobile radio channels, and compared to conventional voice-only systems, provides a tripling in voice capacity and additionally provides full capacity for data communications. Additionally, the invention provides a low cost solution to the congestion problems currently being experienced by public and private land mobile radio system users.